The present invention is directed to the process for the removal of organic contaminants, in particular polychlorinated biphenyls (PCBs), from soil, sediments and sludges. All organic compounds having physico-chemical characteristics similar to PCBs can be removed by this process.
Contamination of sediments and sludges of various harbors, rivers and lagoons throughout the United States with PCBs and other organics is recognized to be a serious environmental problem. Specific PCB contamination sites of particular severity have been identified at Waukegan, IL. and Bedford Harbor, ME., the Hudson river in New York and numerous industrial lagoons. Dredging to decontaminate such harbors/rivers and lagoons is unacceptable until effective disposal/treatment methods for the contaminated sediments become available. The detoxification of such contaminated sediments and sludges at economically acceptable costs presents a serious technological challenge if goals of having no more than 1-5 ppm PCBs in the treated sediments are to be met.
A major problem in the decontamination of soil, sediment and sludges is the high water content often encountered in the environment. This is particularly true if the sediment or sludge has to be dredged from a river basis or a lagoon. Water contents of 80% are not uncommon.
Treatment of PCB contaminated sediments and sludges in an incinerator complying with CFR761.70 is quite energy intensive and costly, if 99.9999 percent destruction and removal efficiencies for the PCBs are to be achieved. Exact costs are difficult to predict because it is uncertain what prices commercial incineration facilities will charge to accept the responsibility of handling such sensitive materials. Current estimates range from $1700 to $2000/m.sup.3 if the cost of disposal of residue from incineration are included. Chemical waste landfill disposal costs incurred when the contaminated sediments or sludges are placed in an authorized chemical waste landfill, are less expensive, but present other difficult problems. There exists therefore a very real need for an alternative process technology which is both technically and economically feasible for the cleanup of these PCB contaminated sediments and sludges.
In many cases, soils and sediments are contaminated with more than one type of organic pollutant. For example, PCBs have been used in a wide range of applications as is shown below in Table A.
TABLE A ______________________________________ Use of PCB Classified to Grade of Aroclor Current use of PCB Grade of Aroclor used ______________________________________ Electrical capacitors 1016 (1221, 1254) Electrical transformers 1242, 1254, 1260 Vacuum pumps 1248, 1254 Gas-transmission turbines 1221, 1242 Former use of PCB Hydraulic fluids 1232, 1242, 1248, 1254, 1260 Plasticizer in synthetic resins 1248, 1254, 1260, 1262, 1268 Adhesives 1221, 1232, 1242, 1248, 1254 Plasticizer in rubbers 1221, 1232, 1242, 1248, 1254, 1268 Heat transfer systems 1242 Wax extenders 1242, 1254, 1268 Dedusting agents 1254, 1260 Pesticide extenders, inks, 1254 lubricants, cutting oils Carbonless reproducing paper 1242 ______________________________________
Many different fluids, engineered to work with each of these applications, have found their way into the environment. The presence of these various fluids represent a hazard to the environment even if no PCB contamination were evident.
Another environmental pollution issue of enormous proportion stems from underground storage tanks. It has been estimated that there are between 100,000 and 400,000 leaking underground storage tanks in the USA alone containing many types of chemical substances in the class of petroleum hydrocarbons such as auto and aviation gasolines, heating oils and solvents. In addition to these, a large number of chemicals are stored in underground tanks in the U.S. The following Table B is a list representing about 10% of the total number of these chemicals:
TABLE B ______________________________________ Partial List of Chemicals Stored in Underground Storage Tanks in the United States ______________________________________ Benzanthracene Nitropropane Chloronaphthalene o-Chlorophenol Cresols PCB (Aroclors) Chrysene Phenol Dichlorobenzenes Propylenedichloride Dinitrobenzenes Tetrachloroethylene Dioxane Toluene Epichlorohydrin Trichloroethane Fluoranthene Trichloroethylene Methylethylketone Vinylidenechloride Nitrophenols Xylenes ______________________________________
For every one of these chemicals, there is an optimum solvent or solvent mixture best suited to remove it from soils or sediments. This solvent is often a non-polar hydrocarbon solvent such as hexane, petroleum ether, kerosene, toluene, xylene or a mixture of these. These solvents however tend to perform very poorly if applied to remove organic pollutants from soils and sediments if even small amounts of water are present. The present invention is directed toward the removal of hydrophobic organic compounds (HOC) such as those mentioned listed above from wet soils, sediments and sludges.